Battery pack

ABSTRACT

A battery pack is disclosed. The battery pack includes a battery; a current detecting unit which detects charging and discharging currents of the battery and outputs an analog signal corresponding to the charging and discharging currents; a modulating unit which modulates the analog signal to be a PDM (pulse density modulation) signal by applying a PDM modulation to the analog signal; a memory in which a conversion program for converting the PDM signal into PCM (pulse code modulation) data and a remaining battery charge calculating program for calculating a remaining battery charge by accumulating the PCM data are stored; and a CPU, which converts the PDM signal into the PCM data which are digital data by being supplied the PDM signal from the modulating unit while executing the conversion program stored in the memory, and calculates the remaining battery charge by accumulating the PCM data while executing the remaining battery charge calculating program stored in the memory.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a battery pack which measures aremaining battery charge.

2. Description of the Related Art

Recently, lithium-ion batteries have been loaded in mobile devices, forexample, a digital still camera. In the lithium-ion battery, generally,it may be difficult to detect a remaining battery charge by its voltage.In order to detect the remaining battery charge of the battery, there isa method in which charging and discharging currents in the battery areaccumulated (refer to Patent Document 1).

Since a current is consumed even if the lithium-ion battery is detachedfrom the mobile device, a user needs a detector that detects theremaining battery charge by accumulating the charging and dischargingcurrents of the lithium-ion battery, a regulator/protection circuit, andso on which are contained in a case as a battery pack.

In the detector, analog signals such as current values are convertedinto PCM (pulse code modulation) data which are digital values formed ofmulti bits, and the PCM data are accumulated. Consequently, ananalog-to-digital converter is required to convert detected charging anddischarging currents of the lithium-ion battery into the PCM data (referto Patent Documents 2 and 3).

[Patent Document 1] Japanese Laid-Open Patent Application No.2001-174534

[Patent Document 2] Japanese Laid-Open Patent Application No.2001-102925

[Patent Document 3] Japanese Laid-Open Patent Application No.2003-204267

Recently, the battery pack has been required to be small sizedcorresponding to the miniaturization of the mobile device. However, thecircuit size of an analog-to-digital converter is large; therefore, itis difficult to install the detector in a small sized battery pack.

SUMMARY OF THE INVENTION

The present invention provides a battery pack of a small size which candetect a remaining battery charge of a battery.

According to one aspect of the present invention, there is provided abattery pack. The battery pack includes a battery; a current detectingunit which detects charging and discharging currents of the battery andoutputs an analog signal corresponding to the charging and dischargingcurrents; a modulating unit which modulates the analog signal to be aPDM (pulse density modulation) signal by applying a PDM modulation tothe analog signal; a memory in which a conversion program for convertingthe PDM signal into PCM (pulse code modulation) data and a remainingbattery charge calculating program for calculating a remaining batterycharge by accumulating the PCM data are stored; and a CPU, whichconverts the PDM signal into the PCM data which are digital data bybeing supplied the PDM signal from the modulating unit while executingthe conversion program stored in the memory, and calculates theremaining battery charge by accumulating the PCM data while executingthe remaining battery charge calculating program stored in the memory.With the above structure, a battery pack having a remaining batterycharge function can be realized in a small size.

According to another aspect of the present invention, the CPUintermittently executes the conversion program, loads the PDM signalfrom the modulating unit, and converts the PDM signal into the PCM data.

According to another aspect of the present invention, the battery packfurther includes a voltage detecting unit which detects a voltage of thebattery; a temperature detecting unit which detect ambient temperatureof the battery pack; and a selecting unit which selects one of analogsignals detected from the current detecting unit, the voltage detectingunit, and the temperature detecting unit. The remaining battery chargecalculating program corrects the remaining battery charge by using thePCM data of the voltage detected by the voltage detecting unit and thePCM data of the temperature detected by the temperature detecting unitwhen the remaining battery charge calculating program accumulates thePCM data of the charging and discharging currents.

According to another aspect of the present invention, the modulatingunit is a sigma-delta modulator.

According to another aspect of the present invention, the currentdetecting unit, the modulating unit, the memory, and the CPU areintegrated into one semiconductor integrated circuit.

According to an embodiment of the present invention, a battery pack of asmall size which detects a remaining battery charge can be realized.

Other advantages and further features of the present invention willbecome apparent from the following detailed description when read inconnection point with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a battery pack according to a firstembodiment of the present invention;

FIG. 2 is an exploded perspective view of the battery pack shown in FIG.1;

FIG. 3 is a perspective view of a circuit board shown in FIG. 1;

FIG. 4 is a block diagram showing a fuel gauge IC according to the firstembodiment of the present invention;

FIG. 5 is a block diagram showing a sigma-delta modulator shown in FIG.4;

FIG. 6 is a diagram showing programs stored in a ROM of a memory shownin FIG. 4;

FIG. 7 is a flowchart showing processes in a CPU shown in FIG. 4;

FIG. 8 is a block diagram showing a decimation filter formed ofhardware;

FIG. 9 is a flowchart showing a digital filter process which is executedby the CPU in step S1-3 shown in FIG. 7 in detail;

FIG. 10 is an operations chart according to the first embodiment of thepresent invention;

FIG. 11 is a block diagram showing a battery pack according to a secondembodiment of the present invention; and

FIG. 12 is a diagram showing a connection of a battery pack shown inFIG. 11 with a mobile electronic device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, embodiments of the present invention aredescribed.

First Embodiment

FIG. 1 is a perspective view of a battery pack according to a firstembodiment of the present invention. FIG. 2 is an exploded perspectiveview of the battery pack shown in FIG. 1.

As shown in FIGS. 1 and 2, in a battery pack 100, a battery 101 and acircuit board 102 are contained in a case 103. The battery 101 is, forexample, a lithium-ion battery and is connected to the circuit board 102via connecting terminals 104.

FIG. 3 is a perspective view of the circuit board 102. As shown in FIG.3, in the circuit board 102, a fuel gauge IC 111, a regulator/protectioncircuit 112, a transistor 113, and a current detecting resistor Rs(refer to FIG. 4) are mounted on a printed circuit board 114 having atwo-layer or a multi-layer structure.

The fuel gauge IC 111 detects the remaining battery charge of thebattery 101 by accumulating charging and discharging currents of thebattery 101. The remaining battery charge detected by the fuel gauge IC111 is output to an external mobile device (not shown).

The regulator/protection circuit 112 detects an overcharge, anoverdischarge, an overcurrent, a short circuit, and so on by detecting avoltage of the battery 101 and by detecting a current flowing into aterminal T− (refer to FIG. 4). Further, the regulator/protection circuit112 cuts off the terminal T− from a load by controlling the transistor113 while using the detected result. With this, the battery 101 and theload connected to terminals T+ (refer to FIG. 4) and T− are protected.In addition, the regulator/protection circuit 112 stabilizes andsupplies a power source obtained from the battery 101 to the fuel gaugeIC 111 which is a detector for detecting the remaining battery charge ofthe battery 101.

FIG. 4 is a block diagram showing the fuel gauge IC 111.

The fuel gauge IC 111 is, for example, a one-chip IC and includes adetecting section 121, a sigma-delta modulator 122, a CPU 123, a memory124, and a communication circuit 126.

The detecting circuit 121 includes a voltage detecting section 131, atemperature detecting section 132, a current detecting section 133, anda multiplexer 134.

The voltage detecting section 131 is connected to both terminals of thebattery 101 and detects a voltage of the battery 101. The detectedvoltage is supplied to the multiplexer 134. The temperature detectingsection 132 detects ambient temperature and generates a temperaturesignal corresponding to the detected ambient temperature and outputs thetemperature signal. The temperature signal from the temperaturedetecting section 132 is supplied to the multiplexer 134.

The current detecting section 133 is, for example, a differentialamplifier, and is connected to both ends of the current detectingresistor Rs connected between the battery 101 and the terminal T− viathe transistor 113. With this, the current detecting section 133 detectsa voltage between the ends of the current detecting resistor Rs whichvoltage is generated by a current flowing through the current detectingresistor Rs, and outputs a voltage signal corresponding to charging anddischarging currents of the battery 101. That is, the current detectingsection 133 detects a current flowing in the current detecting resistorRs from a potential difference between the ends of the current detectingresistor Rs.

The voltage is, for example, a reference voltage V0 when the charging ordischarging current does not flow, a voltage more than the voltage V0when the charging current flows, and a voltage less than the voltage V0when the discharging current flows. The voltage signal is input to themultiplexer 134. The signal detected from the current detecting section133 is supplied to the multiplexer 134.

The multiplexer 134 selects any one of the signals from the voltagedetecting section 131, the temperature detecting section 132, and thecurrent detecting section 133 based on a control signal from the CPU123, and supplies the selected signal to the sigma-delta modulator 122.

The sigma-delta modulator 122 applies a PDM (pulse density modulation),that is, a one-bit digital modulation to the analog signal selected fromthe multiplexer 134 and supplies the modulated signal (PDM signal) tothe CPU 123.

The CPU 123 converts the PDM signal into multi-bit digital data, thatis, PCM data by executing a digital filter processing program 147 (referto FIG. 6) stored in the memory 124. In addition, the CPU 123 calculatesthe remaining battery charge in the battery 101 by using the PCM datawhile executing a remaining battery charge calculating program 148(referred to FIG. 6) stored in the memory 124. The CPU 123 is, forexample, a processor such as a microprocessor. The communication circuit116 sends the remaining battery charge in the battery 101 calculated bythe CPU 123 to an external circuit.

[Structure of Sigma-Delta Modulator 122]

Next, the sigma-delta modulator 122 is described. FIG. 5 is a blockdiagram showing the sigma-delta modulator 122. The sigma-delta modulator122 includes a subtractor 141, an integrator 142, a comparator 143, adelay circuit 144, and a one-bit D/A converter 145.

The subtractor 141 obtains a differential signal by subtracting a signaloutput from the one-bit D/A converter 145 from the analog signalsupplied from the multiplexer 134, which analog signal is input to aninput terminal Tin. The differential signal output from the subtractor141 is supplied to the integrator 142.

The integrator 142 integrates the differential signals supplied from thesubtractor 141. The integrated signal output from the integrator 142 issupplied to the comparator 143.

The comparator 143 compares the integrated signal with the referencevoltage V0 set therein. When the integrated signal is larger than thereference voltage V0, the comparator 143 outputs a high level signal,and when the integrated signal is smaller than the reference voltage V0,the comparator 143 outputs a low level signal.

The signal from the comparator 143 is output from an output terminalTout and also is supplied to the delay circuit 144. The delay circuit144 delays the signal output from the comparator 143 by one samplingperiod and outputs the delayed signal.

The delayed signal is supplied to the one-bit D/A converter 145. Theone-bit D/A converter 145 applies one-bit D/A conversion to the delayedsignal and supplies the converted signal to the subtractor 141.

From the output terminal Tout of the sigma-delta modulator 122, themodulated signal (PDM signal) is output, that is, a signal is output inwhich one-bit digital modulation (PDM modulation) is applied to theanalog signal output from the multiplexer 134.

The PDM signal output from the output terminal Tout is supplied to theCPU 123. The CPU 123 executes a program stored in the memory 124 for thePDM signal.

[Data in Memory 124]

The memory 124 is formed of a storage medium having a relatively smallcapacity of approximately 2 KB, such as a ROM and a storage medium suchas a RAM. Programs which are executed by the CPU 123 are stored in theROM. FIG. 6 is a diagram showing programs stored in the ROM of thememory 124. As shown in FIG. 6, in the ROM, the digital filterprocessing program 147 and the remaining battery charge calculatingprogram 148 are stored. The RAM is used as working storage and so onwhen the CPU 123 operates.

The digital filter processing program 147 applies a digital filterprocess to the PDM signal output from the sigma-delta modulator 122,that is, converts the PDM signal output from the sigma-delta modulator122 into PCM data (multi-bit digital value). In other words, the digitalfilter processing program 147 executes, for example, a decimation filterprocess.

The decimation filter process includes a CIC (cascaded integrator-comb)filter process and a FIR (finite impulse response) filter process.Instead of the FIR filter process, an IIR (infinite impulse response)filter process can be used.

The remaining battery charge calculating program 148 calculates theremaining battery charge in the battery 101 by accumulating the PCM dataconverted by the digital filter processing program 147, and stores thecalculated remaining battery charge in the memory 124.

[Processes in CPU 123]

Next, processes in the CPU 123 are described. FIG. 7 is a flowchartshowing the processes in the CPU 123. The CPU 123 intermittentlyexecutes the processes so as to reduce power consumption by using abuilt-in interrupt timer.

First, when a timer interrupt occurs (YES in S1-1), the CPU 123 loads aPDM signal from the sigma-delta modulator 122 (S1-2). The CPU 123generates the timer interrupt every predetermined period correspondingto, for example, an 8-bit string of the PDM signal (for example, every 1ms).

Next, the CPU 123 applies a process corresponding to the digital filterprocessing program 147 to the loaded PDM signal (S1-3). With this, thePDM signal loaded from the sigma-delta modulator 122 is converted intoPCM data (multi-bit digital value).

At this time, the CPU 123 sequentially loads the PDM signals based onthe analog signals output from the voltage detecting section 131, thetemperature detecting section 132, and the current detecting section 133by controlling the multiplexer 134. Then the CPU 123 sequentiallyconverts the loaded PDM signals into the PCM data by executing thedigital filter processing program, and stores the PCM data in the memory124.

Next, the CPU 123 calculates the remaining battery charge in the battery101 based on the voltage values, the temperature values, and the currentvalues (voltage values measured from current vales) which are convertedinto the PCM data by executing the remaining battery charge calculatingprogram (S1-4). For example, the remaining battery charge is calculatedby accumulating the current values (voltage values measured from currentvales). At this time, the remaining battery charge is corrected by thevoltage value and the temperature value.

[Decimation Filter Process]

Next, a decimation filter process is described. FIG. 8 is a blockdiagram showing a decimation filter formed of hardware. As shown in FIG.8, the decimation filter includes a CIC filter section 151 and a FIRfilter section 152.

The CIC filter section 151 includes three-stage integration circuits153, 154, and 155 connected in a cascade, a decimation circuit 156, andthree-stage differentiation circuits 157, 158, and 159 connected in acascade.

Each of the integration circuits 153, 154, and 155 includes an adder 161and a delay element 162. The adder 161 adds input data and data outputfrom the delay element 162. The delay element 162 delays data outputfrom the adder 161 by one sampling period and supplies the delayed datato the adder 161. Each of the differentiation circuits 157, 158, and 159includes a delay element 163, a subtractor 164, and a divider 165. Thedelay element 163 delays input data by one sampling period. Thesubtractor 164 subtracts data output from the delay element 163 from theinput data, and the divider 165 divides the data output from thesubtractor 164 by N.

The decimation circuit 156 thins out data by extracting the data outputfrom the integration circuit 155 once in N times sampling periods, andsupplies the extracted PCM data to the differential circuit 157.

The PDM signals supplied to a terminal 175 are made to be PCM data bybeing integrated at the integration circuits 153 through 155, anddecimation of N to 1 is performed on the PCM data. Further,differentiation is applied to the PCM data at the differentiationcircuits 157 through 159, then, the PCM data are output.

The FIR filter section 152 includes “i” stages of delay elements 171 ₁through 171 _(i) connected in a cascade, “i” stages of multipliers 172 ₁through 172 _(i), an adder 173, and a decimation circuit 174. Themultiplier 172 _(n) multiplies a coefficient A_(n) by PCM data outputfrom the delay element 171 _(n) (n is an integer from 1 to “i”). Theadder 173 adds outputs from the multipliers 172 ₁ through 172 _(i).

The PCM data output from the integration circuit 155 are sequentiallydelayed at the delay elements 171 ₁ through 171 _(i) and the delayed PCMdata are multiplied by the coefficient A_(n) at the multiplier 172 _(n),and the multiplied PCM data at the multipliers 172 ₁ through 172 _(i)are added at the adder 173. The decimation circuit 174 thins out the PCMdata output from the adder 173 by extracting once in M times samplingperiods (decimation of M:1). Then the PCM data produced by the digitalfilter process are output from a terminal 176.

The decimation filter shown in FIG. 8 formed by hardware is realized bythe digital filter processing program 147 which is executed by the CPU123.

FIG. 9 is a flowchart showing the digital filter process which isexecuted by the CPU 123 in step S1-3 shown in FIG. 7 in detail.

First, the CPU 123 reads PDM signals of, for example, an 8-bit stringfrom the memory 124 and performs the same integration processes as thoseat the integration circuits 153 through 155 to the PDM signals (S2-1).Then, a decimation process of N:1 is applied to the integrated PDMsignals (S2-2). Next, the same processes as those in the differentiationcircuits 157 through 159 are applied to the PDM signals, and theobtained PCM data are stored in the memory 124 (S2-3).

Further, the CPU 123 sequentially reads “i” pieces of the PCM data fromthe memory 124 and “i” pieces of the coefficients A₁ through A_(i)stored in the memory 124 and performs the same processes as those in themultipliers 172 ₁ through 172 _(i) (S2-4). Next, the same process asthat in the adder 173 is applied to the PCM data (S2-5), and thedecimation process of M:1 is applied to the PCM data and the obtainedPCM data are stored in the memory 124 (S2-6).

FIG. 10 is an operations chart according to the first embodiment of thepresent invention. In FIG. 10, time t11, t12, and t13 show the timing oftimer interrupt. When the timer interrupt occurs at the time t11, t12,and t13, the CPU 123 loads a PDM signal from the sigma-delta modulator122 (S1-2). Next, the CPU 123 performs a process corresponding to thedigital filter processing program 147 to the loaded PDM signal (S1-3).With this, the analog signals from the voltage detecting section 131,the temperature detecting section 132, and the current detecting section133 modulated into PDM signals via the sigma-delta modulator 122 areconverted into PCM data.

Next, the CPU 123 calculates the remaining battery charge in the battery101 based on the PCM data obtained in step S1-3 and the calculatedremaining battery charge is stored in the memory 124 (S1-4). Theremaining battery charge stored in the memory 124 is read in response toa request from an external circuit and is transmitted to the externalcircuit via the communication circuit 126.

According to the first embodiment of the present invention, thesigma-delta modulator 122 modulates the analog signal to be the PDMsignal, and the CPU 123 performs the digital filter process on the PDMsignal. With this, PCM data are obtained. That is, instead of using anA/D converter having a complex structure, the sigma-delta modulator 122having a simple structure can be used; further, the CPU 123 cancalculate the remaining battery charge of the battery 101. Since theworkload for calculating the remaining battery charge is low in the CPU123, the CPU 123 can fully execute the digital filter process.

In the first embodiment of the present invention, the detecting section121, the sigma-delta modulator 122, the CPU 123, and the memory 124 areintegrated in one semiconductor chip. However, analog circuits of thedetecting section 121 and the sigma-delta modulator 122, and digitalcircuits of the CPU 123 and the memory 124 can be separated into twochips. The CPU 123 and the memory 124 are integrated in the fuel gage IC111; however, the CPU 123 and the memory 124 can be separated from thefuel gage IC 111.

Second Embodiment

FIG. 11 is a block diagram showing a battery pack according to a secondembodiment of the present invention. As shown in FIG. 11, a fuel gaugeIC 200 includes a digital section 210 and an analog section 250.

The digital section 210 includes a CPU 211, a ROM 212, a RAM 213, anEEPROM 214, an interruption controlling section 215, a bus controllingsection 216, an I2C section 217, a serial communication section 218, atimer section 219, and a power-on resetting section 220. The aboveelements (sections) are connected with each other via an internal bus222.

The CPU 211 controls all the elements in the fuel gauge IC 200 byexecuting programs stored in the ROM 212. With this control, the CPU 211calculates the remaining battery charge by accumulating charging anddischarging currents of a battery. At this time, the RAM 213 is used asworking storage. In the EEPROM 214, trimming information and so on arestored. In FIG. 11, the CPU 211 corresponds to the CPU 123 shown in FIG.4, and the ROM 212, the RAM 213, and the EEPROM 214 correspond to thememory 124 shown in FIG. 4.

The interruption controlling section 215 receives an interrupt requestfrom each element in the fuel gauge IC 200 and generates an interruptbased on its priority and informs the CPU 211 of the interrupt. The buscontrolling section 216 controls the internal bus 222 so that whatelement uses the internal bus 222.

The I2C section 217 executes two-line serial communications by beingconnected to a communication line via ports 231 and 232. The serialcommunication section 218 corresponds to the communication circuit 126shown in FIG. 4, and executes one-line communications by being connectedto a communication line via a port 233.

The timer section 219 counts system clocks and the CPU 211 refers to thecounted system clocks. The power-on resetting section 220 resets all theelements in the fuel gauge IC 200 by generating a resetting signal whiledetecting a voltage Vdd which is supplied to a port 235.

The analog section 250 includes an oscillating circuit 251, a crystaloscillating circuit 252, an MPX (multiplexer) 253, a frequency divider254, a voltage sensor 255, a temperature sensor 256, a current sensor257, an MPX 258, and a sigma-delta modulator 259.

The oscillating circuit 251 is an oscillator having a PLL circuit andoutputs an oscillation signal of some MHz. The crystal oscillatingcircuit 252 outputs an oscillation signal of some MHz by being connectedto an external oscillator via ports 271 and 272. The oscillationfrequency of the crystal oscillating circuit 252 is more precise thatthat of the oscillating circuit 251.

The MPX 253 selects one of the oscillation signals from the oscillatingcircuit 251 and the crystal oscillating circuit 252 based on a selectionsignal supplied from a port 273. Then the MPX 253 supplies the selectedoscillation signal to each element including the frequency divider 254in the fuel gauge IC 200. When the selection signal is not supplied fromthe port 273, the MPX 253 selects the oscillation signal from, forexample, the oscillating circuit 251. The frequency divider 254generates clocks by dividing the system clock and supplies the clocks tothe elements in the fuel gauge IC 200.

The voltage sensor 255 detects a voltage of batteries (lithium-ionbatteries) 301 and 302 externally connected to corresponding ports 274and 275, and supplies the detected analog voltage signal to the MPX 258.The temperature sensor 256 detects ambient temperature of the fuel-gaugeIC 200 and supplies the analog detected temperature signal to the MPX258.

A current detecting resistor 303 is connected between ports 276 and 277,the current sensor 257 detects a current flowing in the currentdetecting resistor 303 based on a potential difference between the ports276 and 277, and supplies the detected analog current signal to the MPX258.

The MPX 258 sequentially selects the detected analog voltage signal, thedetected analog temperature signal, and the detected analog currentsignal, and sequentially supplies the selected signal to the sigma-deltamodulator 259. The sigma-delta modulator 259 converts the detectedsignal into a PDM signal by applying sigma-delta conversion to thedetected signal. Then, the sigma-delta modulator 259 supplies the PDMsignal to the CPU 211 via the internal bus 222. The CPU 211 converts thePDM signals into PCM data by performing a digital filter process. Inaddition, the CPU 211 calculates the remaining battery charges byaccumulating the charging and discharging currents of the batteries 301and 302. At this time, the detected temperature signal is used fortemperature correction.

In FIG. 11, the voltage sensor 255 corresponds to the voltage detectingsection 131 shown in FIG. 4, the temperature sensor 256 corresponds tothe temperature detecting section 132 shown in FIG. 4, and the currentsensor 257 corresponds to the current detecting section 133 shown inFIG. 4. In addition, the MPX 258 corresponds to the MPX 134 shown inFIG. 4, the sigma-delta modulator 259 corresponds to the sigma-deltamodulator 122 shown in FIG. 4, and the current detecting resistor 303corresponds to the current detecting resistor Rs shown in FIG. 4.

In FIG. 11, a battery pack 300 is formed by containing the fuel gauge IC200, the batteries 301 and 302, the current detecting resistor 303, aregulator/protection circuit 304, a resistor 305, and an SW (switch) 306in a case 310. The positive electrode of the battery 301 and the powersource input terminal of the regulator/protection circuit 304 areconnected to a terminal 311 of the battery pack 300, and the powersource output terminal of the regulator/protection circuit 304 isconnected to the port 235 of the voltage Vdd which is a power source tothe fuel gauge IC 200. A terminal 312 is connected to a ground terminalof the regulator/protection circuit 304 via the resistor 305, and isconnected via the SW 306 to a connection point where the currentdetecting resistor 303 connects with the current sensor 257 via the port277. The regulator/protection circuit 304 stabilizes a voltage betweenthe terminals 311 and 312 and protects the battery pack 300 when thevoltage becomes a value exceeding a predetermined range by cutting offthe SW 306.

In addition, a connection point where the current detecting resistor 303connects with the current sensor 257 via the port 276 is connected to aport 236 of a power source Vss. The ports 231 and 232 of the fuel gaugeIC 200 are connected to corresponding terminals 313 and 314 of thebattery pack 300.

FIG. 12 is a diagram showing a connection of the battery pack 300 shownin FIG. 11 with a mobile electronic device. In FIG. 12, a mobileelectronic device 400 is a mobile device such as a mobile personalcomputer, a digital still camera, and a mobile phone.

The terminal 311 of the battery pack 300 is connected to a terminal 401of a power source Vdd of the mobile electronic device 400, and theterminal 312 of the battery pack 300 is connected to a terminal 402 of apower source Vss of the mobile electronic device 400. In addition, theterminal 313 of the battery pack 300 is connected to a terminal 403 of aclock line L1 of the mobile electronic device 400, and the terminal 314of the battery pack 300 is connected to a terminal 404 of a data line L2of the mobile electronic device 400.

In this case, generally, the mobile electronic device 400 operates as amaster and the fuel gauge IC 200 in the battery pack 300 operates as aslave. In response to a request from the mobile electronic device 400,the fuel gauge IC 200 of the battery pack 300 sends the calculatedremaining battery charge of the batteries 301 and 302 to the mobileelectronic device 400.

Further, the present invention is not limited to the embodiments, butvariations and modifications may be made without departing from thescope of the present invention.

The present application is based on Japanese Priority Patent ApplicationNo. 2006-035594 filed on Feb. 13, 2006 and Japanese Priority PatentApplication No. 2007-022196 filed on Jan. 31, 2007, with the JapanesePatent Office, the entire contents of which are hereby incorporatedherein by reference.

1. A battery pack, comprising: a battery; a current detecting unit whichdetects charging and discharging currents of the battery and outputs ananalog signal corresponding to the charging and discharging currents; amodulating unit which modulates the analog signal to be a PDM (pulsedensity modulation) signal by applying a PDM modulation to the analogsignal; a memory in which a conversion program for converting the PDMsignal into PCM (pulse code modulation) data and a remaining batterycharge calculating program for calculating a remaining battery charge byaccumulating the PCM data are stored; and a CPU, which converts the PDMsignal into the PCM data which are digital data by being supplied thePDM signal from the modulating unit while executing the conversionprogram stored in the memory, and calculates the remaining batterycharge by accumulating the PCM data while executing the remainingbattery charge calculating program stored in the memory.
 2. The batterypack as claimed in claim 1, wherein: the CPU intermittently executes theconversion program, loads the PDM signal from the modulating unit, andconverts the PDM signal into the PCM data.
 3. The battery pack asclaimed in claim 1, further comprising: a voltage detecting unit whichdetects a voltage of the battery; a temperature detecting unit whichdetect ambient temperature of the battery pack; and a selecting unitwhich selects one of analog signals detected from the current detectingunit, the voltage detecting unit, and the temperature detecting unit;wherein the remaining battery charge calculating program corrects theremaining battery charge by using the PCM data of the voltage detectedby the voltage detecting unit and the PCM data of the temperaturedetected by the temperature detecting unit when the remaining batterycharge calculating program accumulates the PCM data of the charging anddischarging currents.
 4. The battery pack as claimed in claim 1,wherein: the modulating unit is a sigma-delta modulator.
 5. The batterypack as claimed in claim 1, wherein: the current detecting unit, themodulating unit, the memory, and the CPU are integrated into onesemiconductor integrated circuit.